Age-related macular degeneration (AMD) is the most common cause of visual impairment among the elderly in the United States. This research aims to find its cause at the molecular level. In AMD, like many other age- related diseases, both genetic risk factors and environmental assaults are key contributors. A prominent genetic change in chromosome 10 has been previously identified to be strongly associated with susceptibility to AMD. This genetic variant is located in the promoter region of a protein, called the high temperature requirement factor A1 (HTRA1). This disease genotype results in an increased expression of HTRA1. We also performed functional studies using the HTRA1 knockout (htra1-/-) mice, and found that the loss of HTRA1 leads to decreased retinal vascular development along with a significant down-regulation of vascular endothelial growth factor (VEGF) expression. Conversely, our experiments show that increased expression of HTRA1 in RPE leads to an AMD-like pathology and elevated VEGF expression. High VEGF stimulates abnormal vascular growth in the retinal pigment epithelium (RPE) layer and Bruch's membrane of the eye, which can result in wet AMD. One of our more recent studies, published in the Journal of Biological Chemistry revealed that the up- regulation of VEGF by HTRA1 is inversely correlated to the down-regulation of a member of the tissue growth factor-beta (TGF-? family called Growth Differentiation Factor 6 (GDF6). The long term objectives of this proposal are to elucidate the molecular mechanism by which HTRA1 contributes to an increased risk of AMD, and to develop potential therapies for AMD. Our hypothesis is that oxidative stress can induce a higher level expression of HTRA1, which contributes to the risk of AMD by regulating signal transduction, vascular development, angiogenesis, and extracellular matrix. Guided by this hypothesis, we propose to conduct studies in following areas: 1) We will investigate how genetic variants can influence the RPE cells to respond to oxidative stress for the expression of angiogenic factors and HTRA1. 2) We will determine whether HTRA1 and oxidative stress impact retinal and choroidal vasculature and pathology. We will also try to determine whether removal of HTRA1 in mouse is protective to oxidative stress enhanced neovascularization in htra1-/- mice and control mice, which will be used to examine morphology and gene expression in the retina and choroid. 3) We will utilize our cloned monoclonal antibodies against HTRA1 to investigate their therapeutic potential by tissue-specific delivery into the RPE cells, aiming to inhibit the abnormal vascular growth. In this scenario, the selected antibody will be converted into a single chain peptide, which will be further evolved to maximize its affinity to HTRA1 and ability to inhibit the protease activity while minimizing its cytotoxicity using a novel protein scaffold evolution technology. A gene therapy strategy will be used to deliver such antibodies into the RPE cells and test their ability to inhibit choroidal neovascularization (CNV) aiming to develop a novel approach to treat wet AMD.